Positive printing, pressure-sensitive material and method of making it



Nov. 22, 1960 J. J. cLANcY Erm. 2,961,334

POSITIVE PRINTING PRESSURE-SENSITIVE MATERIAL AND METHOD OF' MAKING ITFiled June 4, 195'? 2 Sheets-Sheet 1 INVENTORS JOHN J CL/l/VC)l AL 7'0NB. POOLE Romc. WELLS,

NOV. 22, 1960 L J. CLANCY ETAL 2,961,334

POSITIVE PRINTING, PRESSURE-SENSITIVE MATERIAL AND METHOD OF MAKING ITFiled June 4, 1957 2 Sheets-Sheet 2 @AVM/6 C Ohm da/#v6 a Y 40 my #40 4%46 JNVENToRs JOHN J. CLANCY ,4L 7'0/V POOLE ROBERT C. WELLS BY 53M@MUM/VFY United States Patent Ofiline P,;e,ed.N,22, ,960

POSITIVE PRINTING, PRESSURE-SENSITIVE lMATERIAL AND METHOD F MAKING ITJohn J. Clancy, Westwood, Alton B. Poole, Abington, and Robert C. Wells,Arlington, Mass., assignors to Arthur D. Little, Inc., Cambridge, Mass.,a corpora- `tion' of Massachusetts Filed June 4, 1957, Ser. No. 663,415

16 Claims. (Cl. 117-36) This invention relates to a coating compositionand a resulting coated product. More particularly it relates to acoating which is suitable for application to a flexible backing of acolor which is in contrast with the color of the coating, and toacoating which has controllable pressure sensitivity. The coatedmaterial thereby becomes a positive pressure-printing sheet which needsonly pressure to impart clearly defined marks or characters in the areasand shapes Iwhere the pressure is applied.

This application is a continuation-impart of application Serial Numlber612,520, tiled September 27, 1956 in the names of John l. Clancy, DavidW. Lovering, and Robert C. Wells for Opaque Coating and Composition forand Method of Making It.

In the -business world, it is usually desirable to be able to make anumber of copies of documents, such as accounting forms, order forms,bills of lading, bank deposit slips, sales slips, etc. In the generalycourse of making such copies it is customary -to make up sets of sheetswith one-use carbon paper lixed between each consecutive sheet, or to`give each but the last copy sheet a carbon backing. In ,the rst case,carbon paper mus-t be removed and destroyed; while in the second case,the copies have permanently aixed to Ithe back side a waxy, usually darkcolored material which can easily rub olf onto objects with which it maycome in contact.

Carbon paper is the product most widely used in industry `to makeduplicate copies of documents. Although it has been used for many yearsand in great volume, carbon paper does not provide good copy quality orcontrast for easy reading, particularly when more than 3 or 4 copies arerequired, or where the copy paper -is heavy. lt is not surprising,therefore, that much effort has been spent over the years in an attemptto produce an improved method for making a number of copiessimultaneously either by means of writing tools o-r lby mechanicaldevices.

In addition to the use off carbon paper, duplicate copies are sometimesmade by fusing sheets of paper, the top one of which is treated on theunderneath side and the second which is treated on the top side. Whenthese surfaces are contacted and pressure is applied, chemicalscontained in the two coatings will be caused to react to give acontrasting colored mark on the top of the second sheet. This system hasythe disadvantage of requiring surface coatings on the two faces of thetwo sheets which come into contact. In addition, this type ofduplicating paper can prematurely develop color or can lose the coloredmarks already made under certain atmospheric conditions. Moreover, thenumber of copies which can be made by one application of pressure islimited.

In addition to the requirement for making numerous copies there are alsomany needs for marking papers Where duplicate copies are notparticularly important, but where characteristics, such as resistance toheat., normal pressures of handling, and moisture are required.Normally, such marking papers arel wax-coated with a contrasting colorlayer beneath the wax. However, when these materials are exposed toelevated temperatures, the waxy often melts and the mark placed uponlthe paper is obliterated.

It would therefore be desirable to have a product which can Ibe markedby the application of pressure only, i.e., paper orv other materialwhich would not require the deposition of ink, or carbon from carbonpaper, or graphite from a pencil, for example, to make clearly delined,visible marks on' it. In addition, it would also fbe desirable to keepthe process simple by eliminating the need for chemical reactions whichare difficult to control. Such a product needs no carbon paper or carbonbacking on the sheet above it to make tracing copies on it,` nor does itrequire that ythe two contacting surfaces each be coated with a materialwhich will cause a chemical reaction to form a colored mark wherepressure is ap plied. Furthermore, such a ilexible material shouldpossess good resistance to heat, to normal pressures of handling, and tomoisture. Such a product would be particularly well adapted for use asmarking tape which may be exposed to elevated temperatures.

Although normal duplica-ting methods provide for black o-r darklycolored tracings on a light or white colored background, it would alsobe desirable to have exibility in color, both with respect to [thebackground which in the case of the product of this invention isactually the coating on the exible material, and with respect to thecolor of the tracing which is the original color of thebacking'material.

In order to make a flexible positive pressure-printing material of sucha nature, i.e., one coated with a composition of contrasting color, itis necessary to use a coating composition which itself remains flexibleafter drying. This in turn means providing a coating composition withspecial characteristics.

It is therefore an object of this invention to provide a positive,pressure-printing' material on which clearly and sharply contrastingmarks or indicia may be made by application of pressure alone.Among'other objects of this invention may be listed:

To provide a positive pressure-printing material `which is resistant tonormal pressures of handling, to heat, and to moisture;

To provide a means for making multiple copies of a document =by merelyapplying pressure simultaneously to a number of sheets of positivepressure-printing material arranged on top of each other;

To provide a Way for making multiple copies off a document which doesnot require the use of carbon paper, carbon backing or the necessity toeffect a chemicalreaction, and thereby to provide a means for making agreater number of copies and/ or more distinct copies than previouslypossible;

To provide an opaque coating which may be applied to a ileXib-le backingof a contrasting color and which will form an optical contact with the.contrasting backing material when pressure is applied by means of amanual writing tool, or by mechanical devices using type, etc.;

To provide a vmaterial which can Ibe markedlbypressure alone and whichis resistant to heat, 'thus making it suitablefor use in labellingobjects which are to be exposed to elevated temperatures;

To provide a` coating composition which when deposited on a exiblebacking will not detract from or lessen the flexibility of the backing;and

To provide a coating composition which will furnish the required opaquebackground when dried, but which contains essentially no pigment, andwhich at the same time scatters light to give a white or coloredsurface.

These and other objects will become apparent in the followingdiscussion.

In the following description the term positive pressure-printingmaterial will be used to designate the product of this invention. Theapplication of pressure to the coated backing material causes the colorof the backing material to show where the pressure was applied, thusresulting in a positive mark on the material, and giving the product thename applied hereinafter.

Other terms are used in the description which should be defined. Thus,the terms marks or indicia are used to indicate the configurations,shapes, or areas which are impressed upon the positive pressure-printingmaterial as the result of pressure application. It is desirable thatthese marks or indicia have good copy quality which may be defined interms of clearness or sharpness of outline and that they exhibit goodcopy contrast, ie., contrast in the colors of the background and of themarks or indicia. This contrast does not necessarily have to be betweenwhite and black, any color contrast being suitable. Finally, the termbacking or support is used to designate the material on whose surfacethe coating is applied. It will normally be such as paper or a thinplastic film, but it need not be.

The positive pressure-printing material of this invention is comprisedof a exible backing or Support on one side of which is deposited acavernulous coating which when pressure is applied is permanentlycompressed and is believed to make optical contact both between 'thediscontinuities of the coating and with the backing material at thepoints, lines, or areas of pressure application. Such optical contactpermits the color of the backing material to show through as contrastingtracings with respect to the color of the coating.

The coating composition of this invention comprises:

(l) material capable of forming a light scattering opaque matrixhereinafter referred to as the matrix material;

(2) material which itself is transparent or translucent and suficientlycohesive to form the necessary permanent optical contact within thecoating and with the backing on which the coating is applied,hereinafter called the transparentizing agent;

(3) a liquid in which the matrix material is soluble or dispersible andwhich forms the so-called continuous phase of an emulsion;

(4) a liquid, in which the transparentizing agent is usually andpreferably soluble or dispersible, which forms the so-calleddiscontinuous phase of an emulsion;

(5) an emulsifying agent; and

(6) a water insolubilizing agent for the matrix materials.

Of these, the emulsifying agent may be eliminated under certaincircumstances, and the use of the insolubilizing agent is optional anddepends on the desired properties of the final coating.

A coating composition comprising an emulsion of the above listedcomponents is applied to the surface of the backing material in such amanner as to produce throughout the nal dry coating a multiplicity ofairmatrix interfaces, thus causing incident light to be scattered by thecoating to give a surface of high relative brightness. These air-matrixinterfaces in turn are formed by applying the coating in such a mannerthat when it is in final dry form, the matrix material is throughout aminutely porous or cavernulous lm which appears to be smooth andhomogeneous to the naked eye, but which under a powerful microscopeseems to the liquid forming the discontinuous phase.

include a multiplicity of air spaces, the longest dimension of which ispreferably not over 5 microns. These air spaces are formed by applyingthe coating in the form of a continuous liquid phase in which isdispersed another liquid forming a discontinuous phase.

The transparentizing agentiis believed to form an extremely thintranslucent or transparent film or covering at the air-matrixinterfaces. When sharp pressure is applied to the coating surface inorder to make marks or indicia on the paper, it may be assumed that thematrix material is at least partially pushed aside and compressed, andthat the transparentizing agent permanently welds one air-matrixinterface to another and at the same time welds the now-compressedmatrix material to the backing material. The optical contact thus madepermits the color of the backing material to show through as a sharplydefined mark which exhibits good copy quality.

The liquids of the composition are so chosen that the liquid comprisingthe continuous phase can be vaporized at a temperature lower than thatrequired to vaporize inasmuch as the matrix materials suitable for thecoating composition of -this invention are soluble in water, water maybe used to form an aqueous solution to be used as the continuous phase,thus keeping the overall costs of the coating to a minimum.

In order to render the `final coating water-insensitive, a modifyingagent may be added according to wellknown procedures to either reactwith the matrix material to form an insoluble salt or to cause certaincrosslinking of the matrix material molecules so as to impart waterinsensitivity.

` The coating composition of this invention may then be described as atwo-phase liquid emulsion essentially devoid of pigment, comprising anaqueous solution or 'A dispersion of a matrix material as a continuousphase (which may or may not contain an additional modifying agent suchas a water-insolubilizing agent), and a liquid having a vapor pressuregreater than that of water at f the drying temperature (preferablycontaining -the transparentizing agent) as a discontinuous phase.

' Although it is preferable to have the transparentizing agent in thediscontinuous phase liquid, it is possible, under certain conditions,-to introduce it in the continuous phase liquid.

In addition to the modifying agent used to render the nal coating waterinsensitive, it may be desirable or necessary in accordance with knownpractices to use a solubilizing agent to aid in putting the matrixmaterial into an aqueous solution and to add an emulsifying agent todisperse the discontinuous phase liquid in the aqueous matrix solutionor dispersion.

It is important to note that the final opaque coating of this inventionis to be distinguished from coatings which contain discrete and normallyunbroken bubbles. small enveloped liquid particles, or Hakes; fromblushed coatings, such as are heatand pressure-sensitive; from anordinary sizing compound which in itself scatters very little light; andfrom pure wax coatings; or from pressure-resistant coatings which areincluded in our Serial Number 612,520.

The coating composition and the positive pressure-printing material ofthis invention will be more fully described in theV following discussionand with reference to the accompanying drawings in which Fig. 1 is agreatly enlarged cross-sectional representation of a backing materialcovered on one side with the coating of this invention after it has beenapplied, but before any appreciable amount of either liquid has beenexpelled; t

Fig. 2 is the same coated background after the matrix solvent or liquidof the continuous phase is driven off, but before the iinal drying isaccomplished;

Fig. 3 is the same coated background material after drying is completed;

Fig. 4 is a diagrammatic representation of the coated backgroundmaterial of Fig. 3 showing how an applied pressure forms the requiredoptical contact;

Fig. 5 illustrates a manifold of sheets of the positivepressure-printing material of this invention;

Fig. 6 is a cross-sectional representation of one form of a marking tapemade in accordance with this invention; and

Fig. 7 is a cross-sectional representation of another form of a markingtape made in accordance with this invention.

The multitudinous, minute air-matrix interfaces which provide theuniformly cavernulous basic structure of the final coating of thisinvention are formed by rst expelling or driving off the liquid of thecontinuous phase to leave the matrix which contains minute pockets ofthe liquid of the discontinuous phase. The discontinuous phase liquid isthen driven off from the minute pockets to form a structure containingthe air-matrix interfaces. At the same time at which the liquid of thediscontinuous phase is driven olf, the transparentizing agent isbelieved to precipitate or crystallize on at least a portion of thematrix that deiines the discontinuities of the cavernulous film. Thiscoating is in itself transparent or at least translucent and may be ofno more than molecular thickness. This mechanism requires that theliquids forming the two phases are immiscible, and that the liquid ofthe continuous phase is a solvent for the matrix material (in which theterm solvent may refer to the continuous phase of a colloidal solution),and is preferably a nonsolvent for the transparentizing agent. Theliquid of the discontinuous phase is preferably a solvent for thetransparentizing agent and essentially a non-solvent for the matrixmaterial.

Due to the nature of the matrix material and to the manner in which thetransparentizing agent -is applied, and to the fact that the matrixmaterial itself is a light-scattering material, there are no distinctflakes or scales formed as in a process where flakes are added to anadhesive material and actually attached to the surface to be coated,such as, for example, in U.S. Patent No. 1,922,548. In fact when thecoating of our invention is thoroughly dry, it is glossy and smooth tothe touch. Scraping lightly with a 'knife-edge or the back of afingernail, for example, raises no particles and leaves no traces. Thisiilm, in fact, can best be characterized as being very much like a whitecellophane or a glossy white paper. Photographs made by the electronmicroscope show little pockets elliptical in cross-section and shape,one to two microns long and about one-half micron wide or high. Most ofthese pockets appear to be ruptured, presumably as a result of expellingthe liquid of the discontinuous phase in proper sequence.

The mechanism of the formation of the air-matrix inter-faces and of therole of the transparentizing agent may be explained, in a muchsimplified manner, with references to Figs. 1 through 4 in which likenumbers refer to like elements.

In these iigures backing 10, such as a colored tissue paper, is coatedwith a layer of coating composition 12 formulated in accordance withthis invention. In Fig. l coating composition 1.2 is made up of thecontinuous phase 14, for example, an aqueous dispersion of casein as thematrix material, and minute globules or pockets 16 of the liquid of thediscontinuous phase such as xylene containing paraffin, for example, asthe transparentizing agent dissolved therein.

In Fig. 2, wherein a large portion of the matrix material solvent (whichis the liquid of the continuous phase) has been driven orf, the coatingcomprises the matrix 1S and minute pockets 16 of the liquid of thediscontinuous phase. It is believed that after the liquid of thecontinuous phase is driven off, some shrinking of the coating takesplace and the globules 416 probably assume an ellipsoid-like shape.Finally, when the liquid in the globules 1'6 of Fig. 2 is driven off,there remains the air-matrix interfaces 20 which are coated with atranslucent or transparent coating 22 of the transparentizing agent,which probably has precipitated or crystallized out `of ythediscontinuous phase liquid.V These air-matrix interfaces `serve toscatter incident'light to produce the opaque coating of this invention.These interfaces 20 generally vary inmaximurn dimension from aboutone-half to one micron high `or thick and from about one-half to fivemicrons long, depending upon the conditions under which the coating wasformed. It is preferable that no appreciable number of air-matrixinterfaces have a maximum dimension of more than live microns.

In Fig. 4 there is a diagrammatic representation of what is believedtakes place when pressure is applied by means of a writing tool, or typeface, to the coated material of Fig. 3. The indentation made by themarking tool is represented as 24. Pressure applied to the composition12 pushes `some of the matrix aside and forces the coating ydown towardthe backing material 10, thus laminating multiple thin `layers of matrixand transparentizing agent until this welded area occupies a very thinsection 26 which basically outlines the mark made by the pressing tooland which'forms optical contact at point 28 with backing 10. Thus, when-light strikes the coated material it is scattered by the air-matrixinterfaces which have not been disturbed by the pressure making tool sothat the background material is the color of the coating, usually white,while the points or lines where pressure has been applied show up as thecolor of the contrasting backing material 10 by reason of the fact thatthe backing material shows through. Thus, there is in effect the makingof marks or indicia of a contrasting color upon a pleasing whitebackground which is formed bythe coating material.

From the above description of what is believed to be the mechanism 4bywhich the positive pressure-printing material of this invention achievesgood, clear copy, it

may be seen that it would be ,advantageous to have a coatingcomposition, the pressure-sensitivity of which may be varied accordingto the type of pressure to be applied and the number of copies which maybe desired from one pressure application. For example, positivepressure-printing material which is to be typed or printed upon need notbe as pressure-sensitive as that which is to be written on by pencil,pen, or the like. Likewise, if few copies are to be made, the materialneed not be as pressure-sensitive as in the case where a number ofcopies are desirable. In the following `detailed description of thisinvention a number of ways of controlling the degree of pressuresensitvity of the coating will be presented and then summarized.

The components making up the coating composition of this invention maynow be` lfurther described and defined.

The matrix-farming materialV The matrix material of the coating of thisinvention may be any of the Water-soluble or water-dispersiblefilmforming materials which will adhere tightly to the background areato be covered and which will scatter light at its air interfaces to givea bright, continuous surface.V

Generally, the materials which are -suitable to form matrices may bedefined as those materials which assume colloidal dimensions whenpeptized.

Many natural and synthetic materials are suitable as matrix materials,among which may be listed casein, bentonite (a clay which swells inwater), polyvinyl alcohol, methyl cellulose, alpha protein, animal glue,modified starches, sodium silicate, shellac, natural rubber, and thesynthetic rubbers such as acrylonitrile-butadiene copolymers andbutadiene-styrene copolymers.

In the case of matrix materials which are elastic in nature such as thenatural and synthetic rubbers, it is desirable to include at least asmall percentage by weight of matrix materials which are non-elastic innature. This is due to the fact that the elastic matrix materials have atendency to expand and then to subsequently shrink when the liquid ofthe discontinuous phase is driven olf, rather than to break and maintainthe required air-matrix interfaces. Of course, compatible mixtures ofany two or more of the above listed matrix materials may be used.

It is well known that casein or alpha protein, or mixtures of these, canbe put into a Water solution only with the aid of a solubilizing agentwhich is alkaline in nature and results in the formation of awater-soluble salt of the proteins. Such solubilizing agents include,but are not limited to, ammonium hydroxide, sodium hydroxide, sodiumtetraborate (borax), sodium carbonate and trisodium phosphate. Any ofthe known solubilizing agents for casein may be used in the process offormulating the coating of this invention.

When the matrix material components of the coating is a mixture ofcasein or alpha protein and a water-soluble synthetic matrix material,separate solutions of these are prepared. The synthetic materials areput into solution by any appropriate procedure. Thus, for example,polyvinyl alcohol may be mixed by sifting the powder into water which isbeing stirred very rapidly, preferably rapidly enough to form a vortex.The polyvinyl alcohol powder is introduced into the vortex and stirringis continued (usually for about 10 minutes) until the powder iscompletely wetted and dispersed. The dispersion is then heated to atemperature of 195 F. until the polyvinyl alcohol has all gone intosolution. After cooling, the polyvinyl alcohol solution may be mixedwith a casein or an alpha protein solution. Similarly a modified starch(e.g., a hydroxyethyl ether derivative of corn starch) may be put into awater solution.

If the matrix material is sensitive to water, as casein is known to be,it may be rendered insensitive by converting it to a water insolublecondition in the nal coating by the addition of any suitableWater-insolubilizing agent known in the art. In the case of casein thismay be conveniently done by addng to the casein solution an inorganicmetal salt which is appreciably soluble in water and which forms aninsoluble derivative with casein. Such an inorganic metal salt is zincsulphate. The resulting coating then comprises the water-insoluble zincsalt of casein making the iinal coating practically water insoluble.Casein, alpha protein, glue or the matrix mixtures containing one or acombination of these may also be modified by reacting with othermetallic ions such `as copper, aluminum or chromium to formwaterinsoluble products.

The amount of modifying agent to be added is based upon the assumptionthat a reaction takes place between the modifier and casein (or alphaprotein) as indicated below, using zinc sulphate and ammonium caseinateas examples of the reaction. The ammonium caseinate was, of course,formed when ammonium ions were introduced to aid in solubilizing thecasein.

ZnSO4-l-2NH4 (Caseinate)- Zn (Caseinate) (NH4) 2SO4 Another type ofwater-insolubilizing agent which can be used is exemplified by theaddition of an aldehyde to a coating formulation containing casein orother protein material to react with the protein present through theamino group to form an insoluble cross-linked product. The reaction withan aldehyde may take place before the protein-bearing coating is appliedby adding the aldehyde to the liquid, or after application to the areato be covered by exposing the applied coating to aldehyde vapors, fOl`example formaldehyde. V

Generally the ratio of matrix material to the liquid of thediscontinuous phase will range from about 1:5 to 1:25. The actual ratiowill depend upon the characteristics of the nal coating desired. As arule the more liquid used with respect to the matrix material, thehigher the brightness in the final coating and the more sensitive thecoating will be to pressure.

In preparing the matrix dispersion, it has been desirable to formulatesolutions having from about "5 to 20% solids content by weight.

The following examples (I-III) illustrate the use of three differentmatrix materials and typical formulations of coating compositions inaccordance with this invention. These-examples show the use of aprotein-containing material (casein), a natural occurring hydrophilicclay (bentonite), and a synthetic material (methyl cellulose orMethocel) EXAMPLE I To 10 pounds of water ,(the continuous-phase liquid)was slowly added 3.8 pounds of casein (matrix mater'al) with stirring,and the resulting mixture was permitted to stand for about 20 minutesuntil the casein particles were wetted and swollen by the water. Anadditional 9.2 pounds of water was added and the mixture was heated toabout 160 F. To this heated mixture was added 1.52 pounds of ammoniumhydrox'de (28% NH4OH) as the solubilizing agent, and the batch wasstirred continuously until the casein was completely peptized. Care wasexercised not to overheat the casein solution, and as soon as all thecasein had been peptized the solution was a1- lowed to cool to roomtemperature. In a separate vessel 0.4 pound of zinc sulfate(insolubilizing agent for the matrix material) was dissolved in 1.8pounds `of water and the resulting solution was `added with constantstirring to the cooled casein solution. To this completed solution wereadded 10.7 pounds of water and 10.7 pounds of 28% NH4OH.

In a separate mixing vessel 1.8 pounds of stearic acid (emulsifyingagent) was added to 58.2 pounds of xylene (discontinuous-phase liquid)along with 2.7 pounds of a parain havng a melting point of about 128 F.as the transparentizing agent. The xylene was heated to about 160 F. andmaintained at that temperature until the stearic acid and the parafinicwere completely in solution. This solution of stearic acid and paraffinin xylene was added to the warmed casein solution (120 F.) while thelatter was being stirred rapidly. Stirring was continued until theemulsion had been formed. In this formulation the paraffin i.e., thetransparentizing agent, was present in a concentration equivalent` tolabout 71% of the weight of the matrix material (solid asis).

This coating composition had a viscosity of approximately 2900centipoises. It was applied at a temperature of approximately F. bymeans of a coating roller to a number of samples of 10-pound tissuepaper, the tissue being black or brightly colored such as red, blue,green, etc. The coated paper was then dried in a stream of air heated toF. to form the multitudinous aircasein interfaces required in thecoating. The nal coated tissue was pure white on the coated side and wasrelatively smooth.

A sheet of uncoated tissue and l5 sheets of the material coated asdescribed above were placed contiguously in an electric typewriter andthe top uncoated tissue was typed upon. The resulting l5 copies were alllegible, the last copy having better definition and contrast thannormally associated with the sixth or seventh carbon copy whenconventional one-use carbon paper and tissue paper of the same basisweight are used.

EXAMPLE II Approximately 2.4 pounds of bentonite (sodiummontmorillonite) was stirredinto about 21.6 pounds ofxwater..

9. The mixture was permitted to stand luntil the bentonite had beenswelled and completely peptized. Into this was added 10.8 pounds f ofammonium hydroxide (28% NH4OH). In a separate vessel 3 pounds ofparaffin (melting point about 128 F.) along with 2.15 pounds o-f stearicacid, was dissolved in 65 pounds of xylene heated to about 140 F. Thetwo solutions were rapidly mixed at a temperature of 120 F., the Xylenesolution being poured slowly into the rapidly stirred bentonitesolution. In this formulation the parain was present in a concentrationequivalent to about 125% of the weight of the bentonite (solid basis).This high percentage of paraffin was found to be advantageous in thecase of the bentonite to make the final coating suciently waterinsensitive.

The resulting emulsion had a viscosity of about 1000 cente'poises andwas applied to 10-pound tissue paper by means of a paper-coating roller.The drying of this coating was accomplished in the same manner as thatdescribed for` Example I and the iinal coating created a bright whitesurface which was not overly waxy-like. When pressure was appliedthrough an original, uncoated sheet by either a hand-held instrumentsuch as a pen or pencil, or by type face to the white surface, thereresulted a clear, well defined tracing in the color of the tissue paperbacking on the coated sheet. In Iaddition to producing good copyquality, the final coating of this example exhibited good Water and heatresistance.

EXAMPLE III A dispersion of matrix material was made up by wetting 1.75pounds of methyl cellulose in 17.5 pounds of hot water. When the methylcellulose had been completely wetted, an additional 21.9 pounds of coldwater was added along with 17.5 pounds of ammonia (28% NH4OH). In aseparate vessel the transparentizing agent and the emulsifying agentwere put into solution with the discontinuous phase liquid by adding2.65 pounds of stearic acid and 1.1 pounds of paraffin (melting point128 F.) to 15.7 pounds of Stoddard solvent (mineral spirits having aboiling fraction ranging from 310 to 375 F.). The matrix dispersion wasthen stirred rapidly and into it was added the discontinuous phaseliquid solution until a good emulsion had been formed. To this emulsionwas then added 21.9 pounds of water to adjust it to the properviscosity. This composition was used in coating tissue paper asdescribed in Example I and the nal coating on the tissue paper showedgood copy quality when pressure was applied by typing or printing. Itshowed fair copy quality when pressure was applied by means of a pencil.This is attributed to the fact that the coating was less sensitive topressure than that made with casein as the matrix material, for eX-ample.

T he transparentizing agent The transparentizing agent should be amaterial which in itself is transparent or at least translucent whendeposited in the form of a thin iilm. It should possess certaincharacteristics which enable it to provide the necessary optical contactbelieved to be required in the mechanism described above. It ispreferable, moreover, that it be of such a nature that it can be addedwith the discontinuous phase of the emulsion.

The transparentizing agent may be a liquid, paste or solid so long as itprovides the necessary optical contact. In order to provide thisnecessary optical contact, the transparentizing agent should becohesive, i.e., it should be capable of uniting layers or particles ofitself as well as layers or particles of the matrix material withitself. The requirement for cohesion is illustrated in Fig. 4 in whichthe laminated layer 26 of transparentizing agent and matrix material isshown. The transparentizing agent should also be capable of wetting thematrix material, a property which contributes to its cohesiveness.

10 In order to form the necessary 'indentation v24 (see Fig. 4) whichapparently requires some local vdisplacement of the matrix material andthe transparentizing agent, the transparentizing agent should beplastically deformable or flowable to a degree to permitsuch localizeddisplacement. Moreover, to achieve the maximum effect in contrasts andgood clear copy, the transparentizing agent should be at leasttranslucent when `deposited in a thin tilm and it should have arefractive index of the same order as the matrix material to prevent theformation of scattering interfaces in the final copy. It appears fromthe mechanism which has been postulated for the action Y of thetransparentizing agent that it should possess all,

`or most, of these characteristics to achieve the optical contactbelieved to be necessary.

In addition to achieving optical contact, the transparentizing agent,for practical reasons, is preferably one which will not migrate eitherinto the backing material, the matrix material, or to the surface of thecoating. Although migration does not at first materially reduce theperformance of the final product (i.e., the positive pressure-printingmaterial) it can shorten its useful life if migration is excessive.

The transparentizing agent will normally be water insoluble but solubleor dispersible in the discontinuous phase liquid. It is thereforepreferably introduced by dissolving or dispersing it in thediscontinuous phase liquid. Those transparentizing agents which areinsoluble in water appear to contribute to making the final coating morewater insensitive.

A large number of transparentizing agents have been used in the practiceof this invention. This can be seen in the following example whichcontains a tabulation of the results from a large number of differentcoating formulations prepared in accordance with the practice of thisinvention. Each coating composition was made up in the manner describedin Example IV. A basic casein dispersion was used to form the continuousphase of the emulsion. Xylene was used as the discontinuous phase liquidand different transparentizing agents were used in the formulation.

EXAMPLE IV A basic casein dispersion in water was made by slowly adding3.8 pounds of casein to 10 pounds of water with stirring. The resultingmixture was permitted to stand for about 20 minutes .until the caseinparticles were wetted and swollen by the water. An additional 9.2 poundsof water was added and the mixture was heated to about 160 F. To thisheated mixture was added 1.52 pounds of ammonium hydroxide (28% NH4OH)and the batch was stirred continuously until the casein was completelypeptized. Care was exercised not to overheat the casein solution, and assoon as all the casein had been peptized the solution was allowed tocool to room temperature. In a separate vessel 0.4 pound of zinc sulfatewas dissolved in 1.8 pounds of water and the resulting solution wasadded with constant stirring to the cooled casein solution. To thiscompleted solution was added 10.7 pounds of water and 10.7 pounds of 28%NH4OH.

In a separate mixing vessel 57 pounds of Xylene (xylene to casein ratioof 15 to 1) was warmed to about 160 F. and sutiicient stearic acid andtransparentizing agent were added to give the weight percents of solidsin the final coating indicated in the tabulation below. The mixture wasmaintained at this temperature until the stearic acid andtransparentizing agent had gone into solution. This solution of stearicacid and paralin in xylene was then added to the warmed casein solution(at about F.) while the latter was being stirred rapidly. Stirring wascontinued until the emulsion had been formed.

These coating compositions were applied at a temperature of about .85 F.by means of a coating roller to samples of 10-pound tissue paper anddried as in Ex- Y ample' I.

The results, in terms of final coating performance, are tabulated belowfor the different transparentizing agents used in the above basicformulation. The iinalcoating performance is based upon the contrast anddefinition, or copy quality, of marks and indicia placed on the positivepressure-printing material thus made. These results are rated on thebasis of copy quality obtainedwhen pressure was applied by typing and bywriting with pencil or pen on an uncoated topsheet having a number ofEXAMPLE V A dispersion of casein was prepared as described in Example Iand a solution of xylene, stearic acid, and paraffin was prepared alsoas in Example I, except that 0.65 pound of paraiiin was substituted forthe 2.7 pounds of paratiin used in that example. This formualtion gavesheets of the positive pressure-printing paper placed a concentration ofparaffin equivalent to about 17% directly under it.

of the weight of the-casein present. Samples of 10-pound Solids Contentoi Final Coating Quality of Reproduction Physical Form ofTransparentizing Agent Transparentizing Wt. WL. Wt.

Agent Percent Percent Percent Pencil Typewriter Trans. Stearic CaseinAgent Acid Stearic Acid Solid 21 79 Dn do 50 50 Polyamidel Viscousliquid 39 13 48 Pai-aplex- G20 (Alkyd-type polyester).`..- Greaselike..39 13 48 Hycar Liquid 1312 2 Very viscous liquid-.. 17 17 66 39 13 4s 54i0 3e Silicone Fluid 3 (Viscasil, 10,000) 39 13 48 Pale Oil 1000 39 1348 do Do. Lanolin, anhydrous 39 13 48 Fair-Good.. Poor-Fair. Blown SoyoBean Oil Fa "f gLFar 47 21 32 Very Good.`

26 26 48 Do. Parafin, M.P., 128 F- 35 35 27 Do. 33 21 46 Do.

, 71 10 19 Fair to Good. Mineral Oil 33 2l 46 Fair. Stearamidc Type Wax33 21 46 Do. Polyethylene 33 21 46 Do. Polyglycol Mol. Wt. 4000 33 21 46Fair-Good. Glyccryi Monostearfit e w 33 2l 46 Good. Petrolatum 33 21 46Fair. Oxidized Microcrystnlline 33 21 46 Good.

1 l Polymerization prod'iet oi dimerized linoleic acid and aliphaticpolyaniines.

2 Butadiene-ncrylonitrile copolymer. 3 General Electric Company Viscasil10,000.4

It will be seen from the tabulation thatia number of materialspossessing `the-'characteristics discussed make satisfactorytransparentizing agents. The final choice will be` at least partly'determinedwith, respect to the pressure sensitivity desired in the finalcoating. Of the transparentizing agents listed above, and for whichspecic examples are given in the tabulation, `the hydrocarbon wax havinga melting point of about 12S-130 F. is preferred for the practice ofthis invention.

The amount of transparentizing agent will be determined by the degree ofsharpness or definition required in the final tracing on the positivepressure-printing material of this invention. Because of the role of thetransparentizing agent `as a coating for thematrix interfaces, theamount of transparentizing agent will depend primarily on the amount andtype of matrix material present in the iinal coating. v

It has been found `that the amount of transparentizing agent may varyfrom about=10 to 300%` of the weight of the matrix solids present. Apreferred range is from about `to 75% -of the weight of Athe matrixmaterial. lf too little transparentizing agent is presentgthe `desiredetiectobtainable fromthe transparentizing agentis not fully realizedwhile if too much of the transparentizing agent is used, the iinalcoatiugitakes onV the characteristics of a wax rather than a coatingsuitable for apositive pressure-printing material. As exemplified inExample Ill, itmay be desirable to determine the amount oftransparentizing Vagent with respect to the matrix materials used. VForexample, in the case of the bentonite it was desirable lto u'semoretransparentizing agent since it also served in therole of awater-insensitizing agent.

The range of-the transparentizing agent is shown below in'ExamplesfVwand `VI in which hydrocarbon wax with a melting point ofabout 128 F. was usedtinta tissue paper were coated with thiscomposition, dried as described in Example I, and tested for good copyquality. Although pressure applied by means of a pen, pencil, or theface of a typewriter key gave good copy, it was not as satisfactory asfar as optical contact achieved as was the composition of Example I, in`which the parafn was present in about 71% of the Weight of the solidcasein.

EXAMPLE Vl A matrix dispersion was prepared as described in Example Iand a xylene rsolution of stearic acid and paraffin was prepared asgiven also in Example l, except that 3.3 pounds of parain wassubstituted for the 2.7 pounds. This parain was equivalent to about 87%of the solid weight of the casein. The coating composition was prepared,applied, and dried in the same manner as described in Example l. Theiinal dried surface gave good copy quality, excellent water and heatresistance without showing any strong tendency towards being waxy. i i

In additionto using 'a material which` serves only as a transparentizingagent, it should be pointed out that the emulsifying agent, if present,can also serve as: a transparentizing. agent. The quantity ofemulsifying agent thus serving in an alternate role is in addition tothe quantity Aof the transparentizing agent specified.

Emulsz'fyng agent The emulsifying agent has a dual role in the coatingcomposition of this invention. It acts both as an aid in forming thedesired` emulsion and also as a transparentizing agent.

Incthe mixingof the coating composition of this in ventionfzailthorouglidispersingof .one liquid` in another is required to form the necessaryemulsion and it is desirable under some conditions `to add anemulsifying agent such as those commonly used to prepare emulsions. Suchemulsifying agents may be one of the appropriate soaps which may bedefined as salts of a strong base such as ammonium hydroxide, or sodiumhydroxide, and o-f a fatty acid such as stearic, palmi'tic, or lauric.The soap used as an emulsifying agent should be one which is a solid atroom temperature in the final form which appears in the coating. Theemulsifying agent can be omitted provided it is not essential to themaking of the emulsion, but it is preferable to have one, inasmuch as itserves also as a transparentizing agent.

The emulsifying agent may be formed in situ by reaction between thefatty acid and an alkali metal ion furnished for example from an excessof a solubilizing agent used in connection with the matrix material.Thus, if a stearic or palmitic acid is added to a coating mixturecontaining an excess of ammonium ions, ammonium stearate or ammoniumpalmate is formed and serves as the emulsifyng agent.

The amount of emnlsifying agent used will be determined fii'st by thequantity required to produce a good emulsion of the continuous phase anddiscontinuous phase liquids, and secondly by the amount desirable tocontribute to the effect of the transparentizing agent. Thus, if noemulsifying agent is required to form the necessary emulsion and noadditional transparentizing effect is required, no emulsifying agentneed be added. However, if an emulsifying agent is required to lform theemulsion and/ or is required in the role of a transparentizing agent,then the amount of emulsifying agent may be as high as about four timesthe weight of the matrix material solids present in the continuous phaseportion of the emulsion. The incorporation of large quantities ofemulsifying agent into the formulation may require an increase in theamount of discontinuous phase liquid. Generally, the desired amount ofemulsifying agent used will vary from about 3 to 10 -percent of theweight of the discontinuous phase liquid containing the emulsifyingagent in solution. l

The following examples illustrate the types of emulsifying agents whichare satisfactory for the process of this invention.

EXAMPLE VII A casein dispersion was first formed by mixing 14.1 poundsof casein, 73.2 pounds of water, and 5.7 pounds of ammonia (28% NH4OH).After the casein had been solubilized, 1.4 pounds of ZnSO4, `dissolvedin 5.6 pounds of water, was added to the casein dispersion. Thedispersion was otherwise made up in the manner described in Example I.To twenty-five parts by weight of this dispersion was added 10 parts byweight of water to dilute it to the proper consistency. In a separatevessel 5.4 pounds of stearic acid, and 2.5 pounds of paraffin (meltingpoint 128 F.) were dissolved in 54 pounds of warm xylene and the mixturewas stirred until complete solution had been obtained. To the 25 partsby weight of the casein solution, now containing the additional l partsby weight of water, was added 7.5 parts by weight ammonia (28% NH4OH)with stirring. Then, onehalf of the xylene solution was added to thecasein dispersion with rapid stirring, an additional 7.5 parts by weightof ammonia was added and finally the remaining portion of the xylene Wasadded and stirred to form the desired emulsion. The resulting coatingcomposition was coated on l0-pound black -tissue in the manner describedin Example I and the coating composition dried in the manner describedalso in Example I. It was possible to make duplicate copies by markingon an uncoated sheet having under it 10 sheets of the coated materialwhen pressure was applied to the top uncoated sheet by a pencil. Withthis material it was possible to make up to some 25 copies by use of atypewriter.

14 EXAMPLE vnr A coating composition was made up exactly as described inExample VII except that an equal weight of palmitic acid was substitutedfor the stearic acid of Example VII. The performance of the coating whenapplied to tissue paper was similar to that achieved by the coatingcomposition containing stearic acid as an emulsifying agent.

EXAMPLE IX The stearic acid in the coating composition of Example VIIWas replaced by an equal Weight of lauric acid and the coatingcomposition treated and handled in the same manner as in Example VII.The resulting coating composition was not as satisfactory aslthatobtained in Example VII in that the whiteness of the coatingproduced was inferior.

EXAMPLE X The stearic acid in Example VII was replaced with an equalweight of oleic acid. The resulting coating composition which was mixed,applied and dried as in Example VII, was not found to be as satisfactorybecause the oleic acid present as an emulsifier was not a solid at roomtemperatures. This, in turn, caused the oleic acid to migrate into thepores of the tissue paper.

Continuous-phase [liquid Liquids suitable for the continuous phase ofIthe emulsion forming the coating of this invention should be solventsfor the matrix material and preferably nonsolvent for thetransparentizing agent. Liquids other than water may be used to form thecontinous phase, but Water Vis preferred for practical and economicalreasons; It should be noted that the use of a water-soluble matrixmaterial, and hence of an aqueous solution as a continuous phase, meansthat the cost of ythe coating composition of this invention can bematerially reduced below the cost of an oil-base paint or a coatingusing an organic vehicle to form the continuousV phase.

Dlscontnuous-phase liquid The liquid forming the discontinuous phasemus-t have a vapor pressure less than that of the liquid forming thecontinuous phase, i.e., usually less than that of water at the dryingtemperature, but for practical purposes it should have a boiling pointnot above 325 F. Such liquids include, but are not limited to, xylene,kerosene, mineral spirits, high-flash naphthas, ketones (such as butylmethyl Iketone and amyl ethyl ketone), paraffin hydrocarbons such asoctane, and the higher boiling acetates such as butyl acetate or amylacetate.

The choice of the liquid forming the discontinuous phase will have someinfluence on the pressure sensitivity of the final coating. Thus, .if aliquid is used for the discontinuous phase which has a relatively highvapor pressure, i.e., fairly close but somewhat below that of water,some of the discontinuous phase liquid Iwill pass off from the coatingsimultaneously with the water leaving less of the discontinuous phaseliquid Within the matrix thus forming smaller globules of the liquidwhich in turn means less distortion of the matrix to form the air-matrixinterfaces. The final result of using a high vapor phase liquid means astrong matrix and hence a more pressure-resistant final coating.

The final choice of theV liquid for the discontinuous phase may alsorequire the consideration of such points as that which will give thebrightest coating for a given weight per unit area of surface for aspecific film-forming material; that which will prove to be the mostcompatible with other components such as the binder, the emulsifyingagent, and any dye or dyes added; and that which will meet certain otherrequirements such as toxicity, inflammability, adaptability toproduction procedures, cost, and the like.

The amount of discontinuous p hase liquid with relation to the amount ofcontinuous phase liquid may vary within the limits which may be used toform `the type of emulsion required, normally an oil-in-water emulsion.The limits on such liquid ratios are well known or can easily bedetermined. Within these physical limitations for obtaining theemulsion, the amount of discontinuous phase liquid may be varied inaccordance with the amount of emulsifying agent added. Thus, dependingon the solubility of the emulsifying agent in the discontinuous phaseliquid, it may `be desirable to use more discontinuous'phase liquid whenthe larger quantities of emulsifying agent are used. i

The amount of discontinuous phase liquid may also be expressed in termsof the weight ratio of discontinuous liquidto matrix material in thecoating composition, i.e., in the emulsion. As noted above in connectionwith the matrix material, this Weight ratio may vary from about :1 to25:1. Generally, the less discontinuous liquid present with respect tothe amount o f matrix material, the more prsure it willrequire tomarkthe iinal positive, pressure-printing material. This is due torelatively large amounts of casein solids in thecoating which make thecoating hard and hence diiicult to break down the porous, cavernulousstructure. Where relatively large quantities of discontinuous phaseliquid, with respect to matrix material, are used, the final structureof the coating is very porous and requires relatively little pressure tomark. `This means that under some circumstances, positivepressure-printing material having a very porous coating maybesubject tounwanted marks brought about in handlingetc. The preferred range of` :1offers a compromise between good copy quality and freedom fromsuchunwanted marks. i i f v Of the discontinuous phase liquids listed'.4above, the preferred liquid is xylene, a liquid which has been`illustrated in Examples Iyand II, and Examples III through X. Example IVillustrates the use of Stoddard solvent with mineral spirits ofa boilingfraction from about 310 to3751=. j j

The use of kerosene is illustrated in the example below.

EXAMPLE A XI The xylene of Example I was replaced with a petroleumfraction boiling between 153 and 200 C., i.e., normally called kerosene.The formulation otherwise was the same as that described for Example Iand the resulting coating was equally satisfactory.

Although it will ordinarily be desirable to use a cornposition whichwill give a white coating on a contrasting dark-supporting sheet, it maybe desirable to use a colored coating and hence have a coloredbackground. The essentially non-pigmented coating of this invention maybe made in any desired color by adding one or more dyes to the coatingcomposition. The dyes may be either of the oil-soluble or water-solubletype added to the appropriate phase of the coating composition dependingupon the effects desired.

The examples given above have illustrated in detail the steps in theprocess of mixing the coating composition of this invention. The processmay be described generally as comprising the steps of forming a solutionor dispersion of the matrix material in the continuous phase liquid,adding a portion of a strong base if it is to bensed to form theemulsifying agent in Vsitu, adding additional continuous phase liquid,preparing a solution of the transparentizing agent and the emulsifyingagent (or the fatty acid portion of the emulsifying agent) in thediscontinuous phase liquid, adding about one-half of the solution to thedispersion of the matrix material in the continuous phase liquid withvery rapid stirring, and finally adding the remaining portion of thestrong base and the solution of the emulsifying agent andtransparentizing agent in the discontinuous phase liquid. If a coatingcomposition of low viscosity isrequired, additional continuous phaseliquid may be added at the end of the mixing to adjust the viscosity. i

The viscosityof the coating composition just prior to application can becontrolled by the amount of continuons phase and discontinuous phaseliquid used and, aS noted above, the viscosity may be iinallyreduced ifnecessary by adding the necessary quantity of continuous phase liquid.

Viscosities of a-wide range have been successfully used, the practicalupper limit being about 2960 centipoises while thepractical lower limitis about 400 to 600 centipoises. The optimum viscosity will bedetermined by such factors fas (1) the method used to coat or apply thecoating composition, (2') the mobility of the matrix material, and (3)the type of backing used to which the coating is applied. `,For example,it would be desirable 3when using aknife coater to employ a coating ofrelatively high viscosity, while when a reverse-roll is' used, coatingcompositions of lower `viscositieswould be desirable. As anotherexample,where casein is the matrix material it is desirable to have acomposition of relatively high viscosity since the casein has a tendencyto be fairly mobile and to work-into `the `fibers of the backing, thus,aetingas asaturant rather thanas a coating. Finally, the viscosityshould be adjusted with relation` to the porosity of the paper and theabsorbing rate of the paper. Papers which do not absorb easily cantoleratecoating compositions of 'lower viscosity. j

Once the coating composition has been thoroughly mixed, it may beapplied to the supporting material by any well-known technique such asrolling, brushing, spraying, printing, and the like. Although thecoating may be dried by atmospheric action only, it is more practical todry it by passing a warm stream of air atabout F. over the coating orover the uncoated side. of the backing material. Other Vsuitable dryingtechniques may of course be used. p

The thicknessof the coating when first applied will rangerfrom about8-10 mils. When drying has been completed, the final coating thicknesswill range from between about 0.2 and 0.5 mil.

The coating composition of this invention may be deposited on a varietyof backing or supporting materials. However, Where the purpose is toproduce a positive `pressure-printing material and achieve production ofa number of copies without the use of any carbon paper or carbonbacking, it is necessary to deposit the coating on relatively thinbacking material; If the final copies are to becolor'ed tracings on awhite background, a white coating will be used over a dark coloredbacking, e.g., black, red, green, blue,`etc. To obtain good clear copyitis` desirable to use a backing which is fairly highly colored.

The backing is, of course, not limited to tissue paper but may be anymaterial or surface on which it is desired to make tracings, etc. Wheremarking tape for example, is to bemade it would be advantageous to use amaterial which has an adhesive on one side.

Although it has been found that the coating composition of thisinvention when appliedto a colored tissue gives good clear copy evenwhenit is theitwenty-tifth copy, it has been-found that the quality `andclarity of the copy may be improved by exposing the sheet after pressureapplication to a very brief heating up 'to temperatures at or belowwhich the wax and the coatingcomposition will melt and flow appreciably.Once paper, to which pressure had been applied and the tracing has beenmade, has been heated the coating becomes practically completelywater-insensitive and heat-insensitive.

It will be noted from the above description that there are a number ofways in which the pressure sensitivity of the coating composition -ofthis invention, and hence the resulting positive pressure-printingmaterial, may be controlled. These may be summarized as follows:

(1*)..The choice of transparentizing agent: in general if thetransparentizing agent is a relatively hard wax-like material the finalcoating will be less pressure sensitive;

(2) The amount of transparentizing agent and/ or emulsifying agent whichmay serve as a transparentizing agent: the greater the ratio oftransparentizing agent and emulsifying agent to the amount of matrixmaterial the more pressure sensitive is the final coating;

(3) The vapor pressure of the liquid forming the discontinuous phase:the higher the vapor pressure, i.e., the closer it approaches the vaporpressure of the continuous phase liquid, the less pressure sensitive thefinal coating will be;

(4) The formation of insoluble material such as sodium caseinate whichtends tomake the coating less pressuresensitive;

(5) The ratio of the binder to the amount of liquid forming thediscontinuous phase: the higher the ratio the more sensitive it is topressure; and

(6) The control of the moisture content of the liquid which in turn isrelated to the transparentizing agent chosen and the amount used.

These factors may be so adjusted as to give a final coating, thepressure sensitivity of which may vary over a wide range. The actualpressure sensitivity of the final coating will be, of course, dictatedby the application to which it is put. For example if the coating is fora positive pressure-printing duplicating paper which is to be used inmultiple sheets for making many duplicate copies the coating should berelatively sensitive to pressure. Likewise, if the pressure is to beapplied by hand tools such as pencils or pens, the coating should bemore pressure sensitive than if pressure is to be applied by mechanicaldevices using type. On the other hand, where the coating is to beapplied to marking tapes where duplicates are not required, a lesserdegree of pressure sensitivity is required because more handling, etc.,may be involved.

This invention contemplates the binding of a number of sheets of forms,pads, or stacks of sheets suitable for making multiple copies by meansof applying pressure to the top sheet without the use of any carbonbacking or interleaving carbon paper. It has been shown for example thatit is possible when pressure is applied by means of a typewriter to makeup to 25 duplicate copies with this type of paper.

A typical such manifold is illustrated in Fig. 5. Sheets of positivepressure-printing material 30 are bound to an uncoated upper sheet 32 atone edge 34 by means of any suitable device such as staples 36. Thesheet may have perforations 38 for easy separation. The sheets 30 may,of course, be white coating on different colored backgrounds so thatcopies can be made with tracings in different colors. This is oftenuseful in business forms where it is necessary to sort out copies forvarious uses. In addition to using coated sheets which give a. varietyof colored tracings, it is also possible to selectively coat portions ofthese sheets so that when pressure is applied to the top sheet,selective marking on the subsequent sheets is achieved.

This invention also contemplates the making of marking tapes bydepositing the coating composition of this invention on a suitableexible backing which is coated with an adhesive on the side notcontaining the coating composition. Two such marking tapes areillustrated in Figs. 6 and 7. In Fig. 6 the coating composition of thisinvention 40 is applied to backing 42 which has a layer of adhesive 44on the other side. This arrangement is suitable if backing 42 is of acolor which exhibits sufiicient contrast to coating 40 to give a goodmark. If backing 42. is not highly colored or is transparent, then itwill be desirable to interpose a colored layer 46 (Fig. 7) to give welldefined marks.

It will be seen from the above description that by the process of thisinvention it is possible to prepare a positive pressure-printingmaterial which can be marked on by means of application of pressureonly, yile., papers or other material which does not require thedeposition of ink or the use of carbon paper or carbon backing. The useof such paper in making up business forms such as bank deposit slips,bills of lading, sales slips, and the like would achieve economicadvantages as well as eliminate the use of carbon paper or carbonbacking. Furthermore, the positive pressure-printing duplicatingmaterial of this invention is such that it does not detract from theflexibility of the original backing or support, eg., paper, and at thesame time possesses good resistance to heat, normal pressures ofhandling, and to moisture.

We claim:

l. A coating composition capable of forming a thin, opaque, essentiallynon-pigmented film on a surface, said composition consisting essentiallyof an oil-in-water emulsion, the continuous phase of said emulsion beingwater containing a hlm-forming matrix material which acquires colloidaldimensions when peptized, and the discontinuous phase of said emulsionbeing an organic liquid which is a non-solvent for said matrix material,immiscible with water and having a boiling point above water andcontaining dissolved therein a plastically deformable transparentizingagent which is a cohesive, highly viscous to solid material, the weightratio of said matrix material to said discontinuous liquid ranging fromabout 1:5 to about 1:25, and said transparentizing agent being presentin an amount equivalent to from about l0 to 300% or' the weight of saidmatrix material.

2. A coating composition in accordance with claim l wherein saiddiscontinuous phase liquid is xylene.

3. A coating composition in accordance with claim 1 wherein saidmatrix-forming material is casein.

4. A coating composition in accordance with claim l wherein saidtransparentizing agent is a paraffin wax melting at about F.

5. A coating composition capable of forming a thin, opaque, essentiallynon-pigmented film on a surface, said composition consisting essentiallyof an oil-in-water emulsion, the continu-ous phase of said emulsionbeing water 'containing a film-forming matrix material which acquirescolloidal dimensions when peptized, and the discontinuous phase of saidemulsion being an organic liquid which is a non-solvent for said matrixmaterial, immiscible with water and having a boiling point above waterand containing dissolved therein an emulsifying agent and a plasticallydeformable transparentizing agent which is a cohesive, highly viscous tosolid material, said emulsifying agent being one which is solid whensaid coating composition forms said film and which is present in anamount ranging from about 3 to 10% by weight of said discontinuous phaseliquid, the weight ratio of said matrix material to said discontinuousliquid ranging from about 1:5 to about 1:25, and said transparentizingagent being present in an amount equivalent to from about 10 to 300% ofthe weight of said matrix material.

'6. A coating composition in accordance with claim 5 wherein saidemulsifying agent is stearic acid.

7. A coating composition in accordance with claim 5 wherein saidtransparentizing agent and said emulsifying agent are the same.

8. A coating composition capable o-f forming a thin, opaque, essentiallynon-pigmented film on a surface, said composition consisting essentiallyon an oil-in-water emulsion, the continuous phase of said emulsion beingwater containing a film-forming matrix material which acquires colloidaldimensions when peptized, and an insolubilizing agent for said matrixmaterial whereby said matrix material becomes substantially waterinsoluble upon formation of said film, and the discontinuous phase ofsaid emulsion being an organic liquid which is a nonsolvent for saidmatrix material, immiscible with Water and having a boiling point abovewater and containing dissolved therein a plastically deformabletransparentizing agent which is a cohesive, highly viscous to solidmaterial; the weight ratio of said matrix material to said discontinuousliquid ranging from about 1:5 to about 1:25, and said transparentizingagent being present in an amount equivalent to from about to 300% of theweight of said matrix material.

`9. A positive, pressure-printing material comprising a iexible` backinghaving deposited on one side thereof a coating characterized by being amatrix of a ilmforming material having uniformly distributed throughoutits entire volume, multitudinous, minute air-matrix interfaces varyingin maximum dimensions from about one-half to one micron with noappreciable number exceeding ve microns providing a uniform cavernulousstructure and containing a plastically deformable transparentizing agentpresent in an amount equivalent to from about 10 to about 300% of theweight of said matrix, said agent being further characterized as acohesive, highly viscous to solid material, said film-forming ma terialbeing a water swellable material which acquires colloidal dimensionswhen peptized.

10. A pressure-printing material in accordance with claim 9 wherein saidcoating is white and said backing is of a color which forms a sharpcolor contrast with said white coating.

11. A pressure-printing material in accordance with claim 9 wherein saidbacking is tissue-weight paper.

12. A manifold of exible sheets joined in superimposed arrangement andsuitable for simultaneously making a number of copies by application ofpressure alone to the top sheet of said manifold, comprising a pluralityof sheets of a flexible material, each sheet under the top sheetconsisting essentially of a exible colored backing having deposited onthe top side thereof a coating characterized by being of a color whichcontrasts with the color of said backing, said coating being a matrix ofa film-forming material having distributed throughout its entire volume,multitudinous, minute airmatrix interfaces varying in maximum dimensionsfrom about one-half to one micron with no appreciable number exceedingve microns providing a uniform cavernulous structure and containing aplastically deformable transparentizing agent present in an amountequivalent to from about 10 to about 300% of the weight of said matrixand being further characterized asia cohesive, highly viscous to solidmaterial, said ilmform ing material being a water swellable materialwhich acquires colloidal dimensions when peptized.

13. A manifold in accordance with claim 12 wherein selected areas ofsaid sheets are coated with said coating.

14. Process for coating a substrate area with a coating composition toform a pressure-sensitive positive printing marking surface, comprisingthe steps of preparing a dispersion of a matrix material in water,preparing a solution of a transparentizing agent in an organic liquid.immiscible with water and having a boiling point above that of waterbut below about 350 F., rapidly stirring said dispersion andsimultaneously adding said solution to form an oil-in-water emulsion,`depositing said coating composition on said tiexible backing material,expelling first a majorportion of said water and forming in theresulting film of said matrix material a multiplicity of small pocketsof said Organic liquid, and then expelling saidorganic liquid thereby toform multitudinous airrnatrixinterfaces while simultaneouslyprecipitating out said transparentizing agent in said air-matrixinterfaces uniformly distributed throughout the volume of said film andwhich range in maximum dimensions from about one-half to one micron withno appreciable number exceeding tive microns, whereby said lm becomesopaque and light scattering; said transparentizing agent being aplastically deformable, cohesive, highly viscous bo solid material.

15. Process in accordance with claim 14 wherein said drying stepscomprise exposing said coating to a warm air stream. v

16. Process in accordance with claim 14 further characterized by thestep of introducing an emulsifying agent into said discontinuous phaseliquid.

References Cited in the le of this patent UNITED STATES PATENTS1,783,442 Mayer et al Dec. 2, 1930 2,299,694 Green Oct. 20, 19422,299,991 Kallock Oct. 27, 1942 2,306,525 Cummings Dec. 29, 19422,310,795 La Piana Feb. 9, 1943 2,374,862 Green Mar. 1, 1945 2,519,660James Aug. 22, 1950 2,648,924 Brewster Aug. 18, 1953 2,655,453 SandbergOct. 13, 1953 2,710,263 Clark et al. June 7, 1955 2,739,909 RosenthalMar. 27, 1956

14. PROCESS FOR COATING A SUBSTRATE AREA WITH A COATING COMPOSITION TOFORM A PRESSURE-SENSITIVE POSITIVE PRINTING MARKING SURFACE, COMPRISINGTHE STEPS OF PREPARING A DISPERSION OF A MATRIX MATERIAL IN WATER,PREPARING A SOLUTION OF A TRANSPARENTIZING AGENT IN AN ORGANIC LIQUIDIMMISCIBLE WITH WATER AND HAVING A BOILING POINT ABOVE THAT OF WATER BUTBELOW ABOUT 350*F., RAPIDLY STIRRING SAID DISPERSION AND SIMULTANEOUSLYADDING SAID SOLUTION TO FORM AN OIL-IN-WATER EMULSION, DEPOSITING SAIDCOATING COMPOSITION ON SAID FLEXIBLE BACKING MATERIAL, EXPELLING FIRST AMAJOR PORTION OF SAID WATER AND FORMING IN THE RESULTING FILM OF SAIDMATRIX MATERIAL A MULTIPLICITY OF SMALL POCKETS OF SAID ORGANIC LIQUID,AND THEN EXPELLING SAID ORGANIC LIQUID THEREBY TO FORM MULTITUDINOUSAIRMATRIX INTERFACES WHILE SIMULTANEOUSLY PRECIPITATION OUT SAIDTRANSPARENTIZING AGENT IN SAID AR-MATRIX INTERFACES UNIFORMLYDISTRIBUTED THROUGHOUT THE VOLUME OF SAID FILM AND WHICH RANGE INMAXIMUM DIMENSIONS FROM ABOUT ONE-HALF TO ONE MICRON WITH NMOAPPRECIABLE NUMBER EXCEEDING FIVE MICRONS, WHEREBY SAID FILM BECOMESOPAQUE AND LIGHT SCATTERING, SAID TRANSPARENTIZING AGENT BEING APLASTICALLY DEFORMABLE, COHERSIVE, HIGHLY VISCOUS TO SOLID MATERIAL.